1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method for transmitting and receiving an ACKnowledgment (ACK) in a wireless communication system.
2. Discussion of the Related Art
A random access-based UpLink (UL) Bandwidth Request (BR) procedure and raging procedure in a conventional wireless communication system will be described below.
FIG. 1 is a diagram illustrating a signal flow for a UL BR operation in a conventional wireless communication system.
Referring to FIG. 1, a Mobile Station (MS) selects a BR code from a set of BR codes among ranging codes and transmits the selected BR code to a Base Station (BS) in order to request a UL bandwidth in step S110. If the MS fails to be allocated UL resources until expiration of a timer which is activated to a contention-based reservation timeout or a value T3 after the transmission of the BR code, it retransmits the BR code. Upon successful receipt of the BR code from the MS, the BS allocates UL resources to the MS so that the MS may transmit a Bandwidth Request (BW-REQ) message in the allocated UL resources in step S120. In step S130, the MS transmits a BW-REQ message to the BS in the allocated UL resources. Upon receipt of the BW-REQ message from the MS, the BS allocates UL resources to the MS in step S140 and the MS transmits data in the allocated UL resources to the BS in step S150.
FIG. 2 is a diagram illustrating a signal flow for a ranging procedure in the conventional wireless communication system.
Referring to FIG. 2, an MS selects a ranging code from a set of initial ranging codes among ranging codes and transmits the selected ranging code to a BS, for initial ranging in step S210. Upon successful receipt of the ranging code from the MS, the BS allocates UL resources to the MS, for transmission of a Ranging Request (RNG-REQ) message in step S220. According to the time status of the ranging code, the BS may transmit a Ranging Response (RNG-RSP) message to the MS. If the MS fails to be allocated UL resources or to receive an RNG-RSP message from the BS until expiration of a timer which is activated to a contention-based reservation timeout or a value T3 after the transmission of the ranging code, the MS retransmits the ranging code.
When being allocated UL resources for transmission of an RNG-REQ message, the MS transmits the RNG-REQ message in the allocated UL resources to the BS in step S230 and the BS replies to the MS with an RNG-RSP message in step S240. Besides initial ranging, there are handover ranging and periodic ranging.
A random access-based UL BR procedure and ranging procedure in a future broadband wireless access system will be described below.
FIG. 3 is a diagram illustrating a signal flow for a UL BR procedure in a future broadband wireless access system.
In the future-generation wireless communication system, a BS supports both a 5-step regular BR procedure and a 3-step quick access BR procedure. The 5-step regular BR procedure may be performed independently of the 3-step quick access BR procedure or as a fallback mode of the 3-step quick access BR procedure.
Referring to FIG. 3, in the 3-step quick access BR procedure, an MS transmits a BR indicator that is selected randomly or according to a predetermined rule and a quick access message including UL BR information to a BS in step S310. The BR indicator may be a BR sequence or a BR code, and the UL BR information may include a Station Identifier (STID), a request size, etc.
The BS transmits an ACK/Negative ACK (ACK/NACK) for the BR indicator to the MS in step S320. Upon successful receipt of the BR indicator and the quick access message, the BS allocates UL resources for data transmission to the MS in step S360 and the MS transmits data in the allocated UL resources to the BS in step S370. The MS may transmit additional UL BR information along with the data in step S370.
In the 5-step regular BR procedure, the MS transmits a randomly selected BR indicator to the BS in step S310. The BS transmits an ACK/NACK for the BR indicator to the MS in step S320 and allocates UL resources to the MS by a Code Division Multiple Access (CDMA) allocation Advanced-MAP (A-MAP) Information Element (IE) so that the MS may transmit a BW-REQ message in the allocated UL resources in step S330.
In step S340, the MS transmits a BW-REQ message in the allocated UL resources to the BS. The BS then allocates UL resources to the MS by a UL basic assignment A-MAP IE in step S360 and the MS transmits data in the allocated UL resources to the BS in step S370. The MS may transmit additional UL BR information along with the data in step S370.
FIG. 4 is a diagram illustrating a signal flow for a ranging procedure in the future broadband wireless access system.
Referring to FIG. 4, an MS transmits a ranging indicator to a BS in step S410 and the BS transmits an ACK/NACK for the ranging indicator to the MS in step S420. In step S430, the BS then allocates UL resources for transmission of an RNG-REQ message to the MS. The MS transmits an RNG-REQ message to the BS in step S440 and the BS replies to the MS with an RNG-RSP message in step S450.
As described above, upon receipt of a random access code such as a BR indicator or a ranging indicator from an MS, a BS transmits an ACK/NACK for the random access code to the MS in the broadband wireless access system. Accordingly, there exists a need for minimizing the overhead of ACK/NACK transmission.